Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!ucbvax!rsre.mod.UK!LAWS From: LAWS@rsre.mod.UK (John Laws, on UK.MOD.RSRE) Newsgroups: comp.protocols.tcp-ip Subject: Re: [John Robinson : Re: TCP performanc...] Message-ID: <11.OCT.1987.00:18:32.LAWS@RSRE> Date: Sun, 11-Oct-87 03:18:00 EDT Article-I.D.: RSRE.11.OCT.1987.00:18:32.LAWS Posted: Sun Oct 11 03:18:00 1987 Date-Received: Mon, 12-Oct-87 21:13:55 EDT References: <[A.ISI.EDU]10-Oct-87.12:40:17.CERF> Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 41 Vint, I guess this reply should be to the John Robinson portion of your msg - but my mailer is not that smart. Concerning CRC checksum computation. More than 17 years ago I read a paper on this topic which used matrix algebra to construct look-up tables. You took your choice - one large table and a simple one line equation, or more smaller tables and more complicated equations. I could still remember enough maths then to follow the algebra through and did a single table version for the CRC-16 checksum. I used it in EIN and passed it around the European centres (there was no chips then for this and most folks were having to do it in one-off hardware of the day). My code implementation for a CTL Modular-One (a UK m/c with some interesting inovations that were to appear in DEC PDP 11) ran at 10 micro-secs per byte and only a little longer in Corai-66. My only export of this to the US was Ed Cain about 2/3 years ago. What does suprise me is the steady rain of papers on this topic which often propose less effective solutions (and also get the algorithm wrong) and never reference this old paper. Just a mo...... ....found it - P E Boudreau and R F Steen (IBM Corp, Research Triangle Park, N.C.) Cyclic Redundancy checking by program. AFIPS Conf Proc Vol.39 1971, pp 9-15 and the latest I just found this week and in my briefcase waiting to be read Georgia Griffiths and G Carlyle Stones The tea-leaf reader algorithm: an efficient implementation of CRC-16 and CRC-32. Comms of the ACM July 1987 Vol.30 No.7 pp 617-620 typos: tbles = tables, Corai-66 = Coral-66 John